Catherine McAuley High School will have to change its name when it officially drops its affiliation with the Roman Catholic Church in July.

The Sisters of Mercy, who founded McAuley, the state’s only all-girls high school, told the school’s operator that it could no longer use the name of the Irish nun who started the religious organization.

Catherine McAuley High School was named for the Irish nun who founded the Sisters of Mercy, which established the school on Stevens Avenue in Portland in 1969.

“We respect the decision, even though we’re disappointed,” Head of School Kathryn Barr said Tuesday.

Barr said the school tried to work with the Sisters of Mercy so it could continue to use all or part of the name, but the organization ultimately decided against it. Messages left with the Sisters of Mercy seeking an explanation for insisting on the change were not returned.

The private school in Portland will start the process of choosing a new name in the coming weeks by seeking suggestions from students, alumnae, parents, teachers and board members.

The school also plans to hold meetings for members of its community to discuss its future. The board of trustees will announce the school’s new name before July 1.

“While I am saddened by the news that the school will have to change its name, the alumnae know that there is so much more to ‘McAuley’ than its name,” said Katharine Faust, a 1996 graduate and co-chairwoman of the school’s alumnae association. “I hope that many young women in the years to come enjoy the opportunities in leadership, education and camaraderie that I remember so fondly about my time at such a fine school.”

Barr said the school is trying to embrace the name change as part of its renewal.

School officials said, however, that many of McAuley’s traditions, including its plaid uniforms, religion classes and morning prayers, would continue.

Heidi Osborn, chairwoman of the board of trustees, said at the time that the Sisters of Mercy were restructuring their organization and control of the school was headed to their national office.

She said that dropping the affiliation would keep control of the school local as it launches new initiatives, including a partnership with the University of New England that allows McAuley students to earn college credits and the incorporation of art and ethics into its STEM – science, technology engineering and math – program.

“Our independence marks the beginning of a new chapter for our school,” Osborn said in a statement Tuesday. “We will signal this momentous occasion by selecting a name that is both worthy of our vision and emblematic of the traditions and values that will continue to ground us.”

The changes come as the school, founded in 1969, is experiencing declining enrollment, dropping from more than 200 students to 120 in the past 10 years.

The Sisters of Mercy’s presence in Maine has diminished in other ways. Once comprising several hundred women who started and staffed schools, orphanages, hospitals and other institutions statewide, the organization had 20 sisters still active in full-time ministry last summer, when it celebrated the 150th anniversary of its founding in the state.

After McAuley High School officially becomes independent, the order’s only formal affiliations in Maine will be Saint Joseph’s College in Standish and Mercy Hospital in Portland.

Catherine McAuley, born in Dublin in 1778, felt a calling to help the poor and built a house and school for homeless women. Although reluctant to form a religious order, she was advised to do so to ensure her work continued.

The Sisters of Mercy was founded in 1831 and now has more than 9,000 congregations worldwide.

“I am confident that the legacy of Catherine McAuley will continue to influence and direct the mission of Maine’s only all-girls high school,” said Faust of the alumnae association. “She was an extraordinary woman who exemplified mercy, leadership and service to others.”